Yar, or yare, is a nautical term that means ready or prepared for action; quick to move. Lots of accidents can happen on a ship if it's not well maintained, if the rigging is a mess, and if items are not fastened. To say that a sailing vessel is yare is a compliment.
In Shakespeare's The Tempest, the boatswain says the ship is in perfect condition:
The best news is that we have safely found
Our king and company: the next, our ship, —
Which but three glasses since we gave out split, —
Is tight and yare, and bravely rigg'd as when
We first put out to sea.
